As a result of the ever increasing use of energy from renewable energy sources, e.g. from wind energy or solar energy, it is necessary to have means of storing the increasingly large amounts of energy produced thereby. As the generation of electrical energy from renewable sources is subject to weather conditions such as cloud cover or wind strength, the generation of electrical energy fluctuates and it is much more difficult to plan for the availability of the electrical energy.
In order to compensate for daily fluctuations and also provide long-term storage on account of the seasonal variations in energy generation from renewable sources, it is desirable to store/buffer the electrical energy generated. Hitherto electrical energy from renewable energy sources, because of their relatively low output, has generally been fed directly into the grid and in some cases conventional power plants have been derated accordingly, making it unnecessary to store the electrical energy from renewable energy sources. For small amounts of generated electrical energy, already known storage batteries, or more precisely lead-acid and lithium-ion batteries or NaS batteries, are available.
An additional form of electrical energy storage is also provided by electrolysis, for example, i.e. a fluid material such as water is at least partially decomposed into its constituent parts and at least one constituent part is stored. If the stored energy is now to be retrieved, two constituent parts, including the stored constituent part, react to produce the original substance. In this reaction, energy is again produced which, converted into electrical energy, can be fed back into the grid as required. Low-temperature electrolyzers with alkaline electrodes or polymer electrolyte membranes have hitherto been used here. However, electrolyzers of this kind are relatively inefficient. In addition, much energy is required for compressing the hydrogen produced during electrolysis if water is electrolyzed into its constituent elements.